THE cancellation last week of “The Unexpected Man,” an eagerly awaited new drama from London, was prompted by a nasty, behind-the-scenes rift between the play’s veteran New York producer and its fast-rising young English director.

The producer, Elizabeth I. McCann, blames the director, Matthew Warchus, for the collapse of the play, which was to have starred noted British actress Eileen Atkins.

“The real culprit is getting off the hook,” McCann told The Post.

“Matthew Warchus has refused to approve any number of actors we have put forward because, like all the young British directors, he is more interested in pursuing a film career than he is in doing a play. He has kept a distinguished actress, Eileen Atkins, dangling for 18 months, and he has wasted a lot of other people’s time and effort.”

“The Unexpected Man” was written by Yasmina Reza, author of the Tony Award-winning “Art,” which Warchus also directed. The play, a hit in London last year, is about a woman who finds herself sitting next to a famous novelist on a train.

Co-produced by the Roundabout Theater Co., it was to have opened in February at the Gramercy Theater on West 23rd Street.

McCann said Warchus “turned down, for whatever whimsical reason he had at the moment,” a number of well-known New York actors who “were eager” to do the play – among them Frank Langella, Ben Gazzara Joseph Sommer and George Grizzard.

Warchus also vetoed Alan Alda, whom he directed in “Art,” McCann said. “And I pleaded with him until I was blue in the face to consider James Earl Jones,” but Warchus was opposed to casting a black actor in the role, she added.

In McCann’s view, Hollywood’s insatiable appetite for new directing talent is rapidly becoming a serious problem for New York and British theater.

“Matthew and all the other flashy young directors are hoping to become the next Sam Mendes,” she said, referring to the young British director of “Cabaret” and “The Blue Room” who recently triumphed in Hollywood with the movie “American Beauty.”

Reached at his home in London, Warchus denied that he was trying to get out of the project to pursue a film career.

“That is sensationally wrong,” he said, noting that he has agreed to direct a revival of “True West” on Broadway this spring.

“There is a group of British theater directors who have had the privilege of exploring film, but for none of us has it dented our love or our commitment to theater,” he said.

Warchus recently completed work on his first movie, “Simpatico,” starring Nick Nolte.

The director accepted responsibility for the cancellation of “The Unexpected Man,” “not because I want to do a movie but because I have a slight block about this project,” he said.

“The person who plays this part must have a chemistry with Eileen as judged by me in my imagination, and I don’t think any of the people who have come on the table have that chemistry in my mind.”

He also said he had reservations about the Gramercy Theater, “which may not be the right space for this play.”

And he denied that he is opposed to casting a black actor opposite Atkins.

“I am completely open to non-traditional casting,” he said. “I am ready to meet James Earl Jones. Liz must have forgotten that.”

Warchus said he still wants to direct “The Unexpected Man” in New York, but “not until I feel all the elements have come into focus.”

But McCann said that she is so angry, she’s ready to jettison Warchus.

“I would do this play in a minute with another director,” she said.

Meanwhile, Vanessa Redgrave, who co-starred with Atkins four years ago in the off-Broadway hit “Vita and Virginia,” has come up with a solution to the problem.

After reading about the demise of “The Unexpected Man” in The Post last week, she phoned Atkins and offered to don a suit and tie and play the role of the male novelist herself.